It is well known, and the subject of ordinary biology text books, that the skin is a complex system with protective epidermal layers, growing endodermal layers, often a keratinous outer layer, systems of glands and follicles and systems for the supply of intracellular and extracellular fluids. Active methods and compositions for treating the skin which do more than provide a passive coating on it, must take account of its complexity.
Skin renewal can be stimulated, as a natural process, by removal of the outer keratinous layer of the skin system. Such removal can be effected mechanically, for example, abrasively by rubs, brushing and even scraping, or shaving. Chemical exfoliation and peeling are effected by agents that interact with the complex structure of the skin.
Known skin-renewal stimulating compositions and agents can provide anti-aging benefits, for example, a reduction of effects such as keratoses, freckles, wrinkles, elastosis and epidermal and dermal atrophy.
Recent years have seen the widespread use, by consumers and professionals alike, of a range of cosmetic and pharmacological formulations providing anti-aging and dermatologically therapeutic benefits. Active ingredients of these formulations typically include an alpha hydroxy acid ("AHA's" in the popular literature) or a retinoic acid ( marketed under the names RETINA or RENOVA, trademarks of Ortho Pharmaceuticals). Some currently available commercial formulations are described in "Mirabella", January 1993, pages 60-61.
Reputable scientific and clinical reports, as well as much subjective evidence have shown that substantial improvements in skin appearance and condition can be obtained by means of skin-renewal stimulating acids. In general terms, these improvements are believed to be attributable to increased rates of skin cell renewal, and the removal of outer layers of dead cells.
It is also well known that skin-renewal stimulating acids can be irritating, and that the irritation they induce is often a long-term effect manifested several weeks after use of the acids. In extreme cases the irritation can be severe, damaging and painful. Hermitte et al. "Aged Skin, Retinoids and Alpha Hydroxy Acids" Cosmetics and Toiletries 107 pp. 63-67 (July 1992) provides a short review of the title subject, with a substantial bibliography of forty references. The disclosures of Hermitte et al. and the references listed therein are herein incorporated by reference thereto. Such disclosure includes details of many skin-renewal stimulating acids that can be used in the practice of the present invention.